The J = 1–0 Transitions of ¹² Ch ⁺ , ¹³ Ch ⁺ , and ¹² Cd ⁺

A new set of laboratory experimental frequencies for the J = 1–0 rotational transition of 12 CH + , 13 CH + , and 12 CD + are obtained by using a liquid nitrogen cooled extended negative glow discharge in a gas mixture of CH 4 and He. These frequencies are found to be significantly different from those reported previously. The unexpectedly large Zeeman effect and the spin-rotation hyperfine interaction for a 1 Σ molecule are observed. The Zeeman effect and the hyperfine interaction appear to be distinctively different for each isotopic species. Theoretical considerations reveal the isotopic dependence of the magnitudes of these effects, and they also provide strong evidence for the identifications.